Print this pageSedimentary Loading of Salt Sheets with and without Subsalt Extension: Results from Finite-Element Modeling
SCHULTZ-ELA, DANIEL D
A salt sheet flows in response to sedimentary loading. This flow and the rate and distribution of sediment accumulation determine which structures form. Important questions about this process are how the roof of the sheet segments by faulting, the effects of subsalt extension, linkages between subsalt and suprasalt structures, the process of salt breakout, and the location of zones of intense fracturing and faulting. Finite-element modeling provides answers to these questions and indicates that suprasalt deformation requires either differential sedimentary loading or regional extension.
Uniform sedimentation on a flat-topped salt sheet causes no appreciable deformation, regardless of the shape of the base of salt. In contrast, a sediment wedge prograding across the sheet initially tilts like a seesaw, but as the roof thickens the depocenter migrates to become a central syncline. Uplift near the basinward tip of the sheet accelerates as adjoining sediments accumulate. Segmentation of the roof depends on formation of early, weak faults. An initial uniform prekinematic layer strongly damps later faulting and growth of structures. Slow sedimentation enhances basinward extension of the salt sheet and increases segmentation of the roof. Uniform sedimentation with regional (including subsalt) extension causes grabens to segment the roof as it subsides relatively uniformly. As the roof thickens, alternate grabens die and counter-regional faults increasingly dominate. Subsalt extension during progradation of a sediment wedge results in more subsidence and sediment accumulation, slower inflation of the salt crest and less likelihood of salt breakout. Suprasalt structures show little linkage to subsalt structures.